How to switch on the key board's light of my computer?

use the shift key

Open the side of the case and look look for a led on the mainboard. It should be on if the power supply is working properly. Have any changes been made inside the computer such as a new video card or harddrive? Perhaps the connector for the power switch has either come of the mother board or has failed.

*******You switch it on from the BIOS set up******

Start the computer
Press delete key to go to "SET UP"
Select advanceD BIOS features
Look for "BOOT UP NUM-LOCK" and set it to ON
Save settings and restart your computer

****Some times its alread switched on by the manufacturer on the mother board*******

If its a Icon Health and Fitness branded treadmill (proform,image ,healthrider etc.)The safety key activates the on off switch for the console. (micro switch activated by safety key)Check for 9-12v going to console. Unless it has a magnet switch. What brand and model ?

if its a desktop check the connections make sure you don't have them switched.

you need to replace the power supply. The fan sound is the fan for the power supply and not the computer. for cheap parts or used goto headgap's. They know what you need and probably even help you replace it yourself.

HI, make sure there isn't a short in the actual outlet wall socket. if the outlet wall socket is in good condition, this will confirm power board failuer.

You will need to replace the power supply board in this unit in this case.

I suppose you can ask for a KVM switch .

I would start by restarting the computer.
If this does not solve the problem you are more then welcome to get back to me and I'll see if I can help you to further solve the problem.